Scagliola is a plaster imitating marbles. It is composed of plaster of Paris and size, with coloring-matters stirred into the mass. This, with different kinds of the finer cements, is much used for wall panels and pilas ters, and for imitation marble pillars. Large interior as well as exterior surfaces are often quite successfully finished in imitation of granite. To accomplish this, after drying the second coat of plaster a coat of lime tinted with umber is applied, and allowed to dry. It is then finished with a wash of lime, and a mineral black is sprinkled on with a brush, to imitate the spots in the granite.
When interior surfaces are intended to be painted, a much-used prepa ration known as " trowelled stucco" is carefully made from fine lime and clear sand. There is also a variety of cements which may, by constant trowelling and wetting, be worked into a very hard surface capable of a polish like marble, and it can be decorated by the painter.
plaster ceilings are to be fixed upon the iinder side of floors or plaster coverings affixed to wooden partitions, the preliminary operation is lathing, or covering the surface to be worked upon with wooden strips or laths. In the United States, laths are generally of split white or yellow pine from 3 to 4 feet long, inches wide, and ,1_< of an inch thick. In England firwood from the Baltic is usually employed. Sawn laths have a uniform thickness and require less labor in finishing the wall, but are more liable to break. Laths of inetal have also been introduced to some extent. A distance of X of an inch between laths allows for shrinkage; when placed closer the clinches are apt to be weak, and when more distant the laths sag- upon ceiling-s and drop off on the sides by their own weight. To obtain a perfectly true surface upon which to attach the laths, the under sides of joists in ceilings or the battens or quartering in walls are provided with a straight edge, and are corrected either by adzing off projections or bv bringing up inequalities by nailing on strips of wood to the requisite height—an operation variously called " furring" or " fir ring." The laths are laid side by side, and the ends should abut and never overlap, being secured by one nail at each end and one at each intermediate point of support.
or late, various metallic substi tutes for wooden lathing have come into use, and have the advantages of affording better adherence of the plaster and of materially lessening the liability of the spread of fire. Of these substitutes, woven wire is one of the most efficient and best known. Perforated sheet iron, either plain or g-alvanized, has also come iuto prominence for the purpose. One of the best of these substitutes is shown in Figures 5, 6 COL 2).
Mouldings and immediately under the ceilings of rooms require special attention. For the cornice moulding, two plaster screeds arc run with the trowel—one on the ceiling and the other on the side walls—at such a distance from the angles that the moulds can slide over them. A thin wooden screed is also temporarily fastened upon the wall as a guide upon which the mould can slide in a straight line. To make the work secure, the laths of the wall are left bare to the width of the cornice, so that the plaster may clinch safely- between them. What is styled " gauged stuff," or plasterer's putty and plaster of Paris mixed care fully for immediate use and in small quantity, is then prepared and thrown rapidly into the angle with the trowel to an amount fitted to fill the mould, which is promptly run over it, cutting away all superfluous material. The mould is then scraped clean and again run over the moulding. The scrap ings can be hastily added to any defective member of the design, and the mould again applied. When the form is found to be perfect, a gloss is given by the brush, and the work- proceeds to another segment of the cor nice. When moulding-s are not continuous, but enriched, they can usually be run as if continuous, with the enrichments added afterward, the latter being castings of plaster of Paris secured into place with cement or screws. Large cornices, panels, and mouldings are sometimes made npon canvas or wirework strained over wooden frames, which can be readily placed in position, the entire work being washed over with the g-auged stuff. Mould ings and skirtings in exposed situations are made of Portland cement, which can, when necessary, be faced with one of the white cements.
Cast centre-pieces, rosettes, brackets, and similar ornaments, are made of thin plaster poured into a mould through an orifice. The moulds are usually in sections, and are made of plaster hardened with glue or shellac. Such ornaments are attached to their places by fresh plaster, and w-hen required are secured with screws, to support the weight. Large central mouldings, either circular or elliptical, are also made by the same method as the cornice, the mould being run from a central point by an arm or trammel upon a screed of the required shape and dimensions. An inter esting departure in this field of decoration has been made by the adoption of sheet metal of elaborately ornamental designs for ceilings, more partic ularly for centre-pieces. These pieces can readily be attached and removed, and, having- no disposition to crack, are superior in durability to the above named plaster-work of the same kind.